A systematic approach to management of hypercapnic respiratory failure is pre-sented. In order to categorize the etiology of the respiratory failure as pulmonary or extrapulmonary, the alveolar-arterial oxygen tension gradient is calculated. In order to choose between conservative therapy (controlled low-flow oxygen administration) and aggressive therapy (intubation and mechanical ventilation), the ratio relating the net change in hydrogen ion concentration to the net change in carbon dioxide tension is calculated. Predicted ratios for acute, chronic, and acute-on-chronic hypercapnia have been reported. When the calculated ratio approximates that of acute hypercap-nia (0.7 or above), aggressive therapy is warranted. When the ratio suggests that the hypercapnia is chronic (0.3 or below), conservative measures will suffice. If the calculated ratio is consistent with acute-on-chronic hypercapnia (between 0.3 and 0.7), conservative therapy should be attempted initially and the patient observed closely. The trends in clinical and arterial blood gas findings then dictate subsequent therapy.
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